According to the Parkinson's disease foundation, more than 1 million Americans have the disease. Now, new research suggests that exposure to pesticides may increase the risk of the disease and that individuals with specific gene variants may be more susceptible. This is according to a study recently published in the journal Neurology.

In a previous study published in PNAS last year, the research team, including Dr. Jeff M. Bronstein of the David Geffen School of Medicine at the University of California, Los Angeles (UCLA), first uncovered a link between Parkinson's disease and a pesticide called benomyl.

Benomyl is a fungicide. Its use was banned by the US Environmental Protection Agency in 2001 after being deemed a possible carcinogen.

The investigators discovered that benomyl blocks an enzyme called aldehyde dehydrogenase (ALDH). This enzyme changes aldehydes that are toxic to dopamine cells into those that are less toxic. If ALDH is blocked, this can play a part in the development of Parkinson's disease.

For this most recent study, the researchers set out to determine whether other pesticides may have a similar effect.

They analyzed 360 individuals with Parkinson's disease from three Californian counties and compared these with 819 people in the same areas who were free of the disease.

The investigators monitored the participants' exposure to pesticides both at work and home. This was done using a geographic computer model based on data from the California Department of Pesticide Regulation.

The researchers also created a laboratory test to determine what pesticides block ALDH in participants.

Pesticides 'increase Parkinson's risk at low concentrations'

The investigators discovered a further 11 pesticides that block ALDH and increase the risk of Parkinson's disease.

They also found that these pesticides increased Parkinson's risk at significantly lower levels that what were being used.

Commenting on the findings, Dr. Bronstein says:

"We were very surprised that so many pesticides inhibited ALDH and at quite low concentrations, concentrations that were way below what was needed for the pesticides to do their job.

These pesticides are pretty ubiquitous, and can be found on our food supply and are used in parks and golf courses and in pest control inside buildings and homes. So this significantly broadens the number of people at risk."

Individuals with genetic variant 'at greater risk'

Furthermore, the researchers discovered that participants who possessed a common genetic variant of the ALDH2 gene were more susceptible to the ALDH-blocking effects of the pesticides, and were two to six times more likely to develop Parkinson's, compared with pesticide-exposed individuals who did not have the genetic variant.

However, the investigators note that individuals who had the genetic variant who were not exposed to pesticides did not demonstrate increased risk of Parkinson's disease.

"ALDH inhibition appears to be an important mechanism by which these environmental toxins contribute to Parkinson's pathogenesis, especially in genetically vulnerable individuals," says Prof. Beate Ritz of the Fielding School of Public Health at UCLA and co-author of the study.

"This suggests several potential interventions to reduce Parkinson's occurrence or to slow its progression," she adds.

The investigators conclude that therapies involving modulating ALDH enzyme activity or eliminating toxic aldehydes should be created. They say these interventions could potentially reduce the occurrence of Parkinson's disease or slow its progression for individuals exposed to pesticides.

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